Conventionally, as a technology for improving the transmission efficiency in radio communication, hybrid automatic repeat request (HARQ) has been disclosed. In the HARQ, a radio base station may perform error correction coding (turbo coding and the like) on data to be transmitted to a radio terminal, and transmit a radio signal including error correction coded data to the radio terminal by using a plurality of time slots.
A maximum number of time slots (hereinafter, referred to as a “maximum slot number”) used for the transmission of the radio signal in the HARQ is switched according to the reception quality of the radio signal in the radio terminal. A downlink transmission rate achieved when a maximum number of slots are used up (are all used) has been defined in the specifications of a radio communication system, and will be referred to as a “defined transmission rate” in the following description.
In general, since a downlink transmission rate is changed according to reception quality in a radio terminal, it is considered to control a transmission rate of data, which is transmitted by a communication destination apparatus (for example, a server or a communication terminal) of the radio terminal, according to the downlink transmission rate.
Here, when a downlink transmission rate measured by the radio terminal is transmitted to the communication destination apparatus, the time difference may occur between a measurement time of the downlink transmission rate and a data transmission time in the communication destination apparatus. Therefore, it is preferable that the radio terminal calculates a predictive value of the downlink transmission rate (hereinafter, referred to as a “predictive transmission rate”) at a future time (that is, the data transmission time in the communication destination apparatus), and transmits the predictive transmission rate to the communication destination apparatus.
As a transmission rate prediction method for calculating a predictive transmission rate, the following method has been disclosed (for example, see Patent Document 1). Specifically, a radio terminal predicts reception quality at a future time based on the reception quality of a current (and previous) radio signal, and a defined transmission rate corresponding to the predicted reception quality (hereinafter, referred to as a “predictive reception quality”) is calculated as the predictive transmission rate.